A relative position of an object with respect to a radar sensor may be determined in that a radar signal is transmitted by the radar sensor and its reflection at the object is received again. The position of the object is generally indicated based on an elevation angle, an azimuth angle, and a distance. For example, a radar sensor may be used on a motor vehicle to detect objects located ahead of the motor vehicle in the driving direction. A coordinate system fixed to the motor vehicle is thereby usually assumed. The azimuth angle is usually determined by the vertical axis with respect to a longitudinal axis of the motor vehicle. Correspondingly, the elevation angle is determined by the transverse axis with respect to the longitudinal axis of the motor vehicle.
The azimuth angle is often determined with the aid of SIMO (single input, multiple output), in particular in close range, when the object is located less than approximately 100 meters away from the motor vehicle. A radar signal is thereby transmitted by a radar antenna and received again by multiple, horizontally offset receiving antennas. Phase differences between the signals of the receiving antennas indicate the azimuth angle. Depending on the necessary horizontal focus of the receiving antennas, these may be placed only relatively far apart from one another, distances usually being used in the wavelength range of the radar signal used. As the number of receiving antennas and the space available for the receiving antennas are usually limited, the azimuth angle may only be determined with limited accuracy and separation capability, and ambiguities (ambiguous solutions) may occur.
U.S. Pat. No. 8,436,763 B2 describes a system of receiving antennas uniformly horizontally offset on a radar sensor for determining an azimuth angle of a reflecting object.
An additional receiving antenna may be provided which has a different vertical height than the remaining receiving antennas. Thus, the elevation angle of the object may be determined. If the additional receiving antenna is used to determine the azimuth angle of the object, then a systematic angular error results in the determined azimuth angle.
An object of the present invention is to provide an improved method for determining the azimuth angle of an object with the aid of a radar sensor. Preferred embodiments of the present invention are described herein.